Outgoing Transport Minister Khaw Boon Wan has dengue, his office said yesterday afternoon.
It is the third time he has been stricken with the mosquito-borne disease. His first brush with the virus was in the 1980s.
Mr Khaw, 67, also had a swab test for Covid-19, and the result was negative. He is currently warded in Singapore General Hospital.
He posted on Facebook yesterday morning that he had been admitted to an isolation ward for observation after developing a fever.
Speculating on his condition then, he said: "Unlikely to be Covid but dengue is possible as my area is a hot zone. Did the swab test just now and hopefully it is a false alarm. I had dengue before, and it was not pleasant.
"Meanwhile, I will just let the body rest and think about retirement!" said Mr Khaw, who announced before the recent general election that he would be retiring from politics.
Mr Khaw lives in the Yio Chu Kang area, which has parts listed by the National Environment Agency as red zones. Red zones are high-risk areas with 10 or more cases.
He only recently finalised negotiations for the Johor Baru-Singapore Rapid Transit System (RTS), and was looking forward to the signing ceremony.
He said that he had also been preparing his office for the next transport minister.
Mr Khaw maintained his sense of humour in his posting, describing a selfie he took with a nasal tube attached as "hilarious".
He was a civil servant in the Health Ministry in the 1970s and 1980s, and senior minister of state for health during the severe acute respiratory syndrome (Sars) outbreak in 2003. He was appointed health minister the next year.
Learning from the painful lessons of Sars, he instituted new processes and extensive preparations to ready Singapore for the next novel disease outbreak, which Prime Minister Lee Hsien Loong said have "served us well when Covid-19 came upon us".
Singapore's dengue outbreak has continued to surge, with the number of infections topping 1,000 cases for the sixth consecutive week.
There were 1,733 infections diagnosed last week, 65 more than the previous week.
Until this year, the highest weekly infection number was 891, in 2014. As of 3pm on Wednesday, there have been 954 infections diagnosed this week since Sunday.
There are now 424 active dengue clusters concentrated mostly in the eastern part of the country.
Nineteen people have died of dengue so far this year, one fewer than the 20 deaths recorded in all of 2019.